1. Field of the Invention
This invention relates to a plant temperature control system.
2. Description of the Related Art
As taught by WO 2002/070873, for example, the temperature control of a catalytic converter (viewed as a plant) of an internal combustion engine can be achieved by defining a plant model for estimating the temperature of the catalytic converter and detecting catalytic converter deterioration by comparing the model output with the output of a temperature sensor installed in the catalytic converter. When the sensor output indicates a temperature lower than the light-off temperature of the catalytic converter, the conventional system uses the temperature sensor output to correct the temperature estimated by the model and controls the fuel quantity and ignition timing of the engine so as to maintain reduced catalyst temperature so long as deterioration of the catalytic converter continues to be observed.
However, the response of a temperature sensor that can bear up under the temperature fluctuation range of a vehicle exhaust system is usually very poor. Therefore, when the temperature estimated value of the plant model is corrected immediately using the output of the temperature sensor as described in the prior art, a miscorrection is liable to be made. A need is therefore felt for a plant temperature control system that enables accurate correction of the temperature estimated value produced by the plant model even when using a temperature sensor of inferior response.